Altitude compensator for fuel pumps



Sepf 3,1946' M. A. 'rRlsLER A 2,406,973

ALTITUDE COMPENSATOR FOR FUEL PUMPS Filed Nov. 2'7, 1942 Snnentor Patented Sept. 3, 1946 ALTITUDE COMPENSATOR FOR FUEL PUM Milton A. Trisler, Indianapolis, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 27, 1942, Serial No. 467,134

An improvement in a pump serving to supply fuel to the engine of an airplane constitutes the subject matter of this invention.

The object of the invention is to provide for maintaining substantially constant absolute pressure, regardless of altitude, on the bypass valve or other pressure regulating mechanism of an airplane fuel pump. Other objects such as simplicity and eiiiciency will be understood from the description which follows.

An embodiment of the invention is shown by the accompanying drawing in which:

Figure l is a transverse section through a fuel pump combined with a bypass and having my improvement incorporated therein.

Figure 2 is a section on line 2-2 of Figure 1.

On the drawing, numeral is used to identify a pump housing. It has an inlet 9 to receive fuel from a suitable source and an outlet I for connection to the carburetor. Between the inlet and outlet is a pump barrel II within which is an eccentric rotor I3 -carrying the blades I5 and spacing roller I1 as in prior pumps. Above th'e housing 5 is a bypass Valve support I9 and above part I9 is a dome-shaped cover 2|, fastening means 23 securing the several parts together as shown.

Part I9 has an upper transverse but apertured wall 25, an intermediate transverse partition 21, and a circular inner tubular part 2S which latter is reduced in diameter at 3l to telescope within a similar sleeve part 33 of body 5. Between pump parts IS and 2| is secured a flexible diaphragm 35. On the under side of the diaphragm is a flanged disc 3'! integral with a tapered wall valve member 39 which engages a valve seat 4I on part 23. When the valve is seated the space above th'e valve and partition 2T is in communication with the discharge side of the pump by a passage i3 in the partitionizl and registering passages 45 and 41 in the pump members I9 and 5 respectively. The tubular part 29 is cut away to form an opening 49 by which the space within said part 29 is in communication through registering passages 5I and 53 in parts I9 and 5 with the low pressure (intake) side of the pump, the side leading from the fuel supply.

The part 2| of th'e assembly is open to the atmosphere at 55. A threaded member 51 in its upper face adjustably positions the upper abutment 59 of a spring 6I. A sealed bellows or aneroid 63 of known construction is secured to abutment 59. Its lower end contacts the diaphragm 35. Spring El is within the bellows and exerts pressure on its lower face and on the dia- 5 Claims. (Cl. 10B- 42) phragm and valve, being operable to bias the valve upon its seat.

The operation of the device is as follows. is important that the absolute fuel pressure for the carburetor should be substantially constant or should not fall 01T in proportion to the decrease of atmospheric pressure with increases in altitudes. To provide for all needs the pump capacity must be such that the pump outlet pressure always tends to exceed the desired carburetor pressure. In consequence the bypass valve is at all times open, at least to some extent. The pressure at the pump outlet in excess of the constant pressure needed opens the valve, the underside of the diaphragm (which is greater in area than the bypass valve) being always in communication with the pump outlet by way of passages 4'I, 45 and 43. 'Ih'e fuel returns to the low pressure side of the pump by way of passage 49 and 53. The constant pressure desired is maintained by the proper adjustment at 51 of springs 6I At sea level the tendency of the sealed evacuated bellows to expand and exert pressure on the valve is partially balanced by the external pressure on the bellows. When the device is used on an airplane, and the apparatus reaches higher elevations the reduced external air pressure permits the bellows spring 6I to exert increased pressure on the valve to maintain the pressure applied to the diaphragm and valve substantially constant. In the absence vof the bellows, the pressure on the valve being the air pressure plus the spring pressure, would decrease as the plane reaches higher altitudes and with decreasing applied pressure the valve would open at too low pump pressures and insuicient fuel would be supplied to the carburetor. It will be observed that the diaphragm 35 performs the important function of preventing the fuel under the pressure conditions determined by the pump from reaching the space around the bellows with the result that the unbalance of air pressures is free to operate as stated.

I claim:

1. In a fuel pump having a pressure regulator by-pass, a valve therefor, a spring and an altitude sensitive aneroid jointly Operable on said valve, an air vented chamber containing said spring and aneroid and a flexible diaphragm connected to said valve and separating said aneroid chamber from said bypass the dimensions of the aneroid and the diaphragm being such that the air pressure within the chamber exerts a force on the diaphragm tending to close the valve substantially equal to the force of said air pressure 3 acting on the aneroid in a direction t0 open the valve.

2. In a fuel pump, means forming a bypass between the high pressure and low pressure sides of said pump, a valve to close said bypass, a spring and an altitude sensitivel aneroid operable jointly to bias said valve to closed position, an air vented chamber containing said aneroid, and a. diaphragm sealing said ch'amber from said by-` pass the dimensions of the aneroid and the diaphragm being such that the air pressure within the chamber exerts a force on the diaphragm tending to close the valve substantially equal, 5.0 the force of said air pressure acting on the aneroid in a direction to open the valve.

3. The invention defined by claim 2, said aneroid comprising a sealed and partially evacu; ated bellows having a fixed abutment, at one end, th'e other end operably associated with said valve to exert thereon variable pressures dependent upon external air pressure.

4. The invention dened by claim 2, together with adjustable means to determine the resilient force applied by said spring.

5. In combination, a fuel pump having a pressure regulating by-pass valve, means forming a chamber associated with said fuel pump, movable means secured to said valve and separating said pump from said chamber, said chamber being open to the surrounding air, a sealed aneroid and a spring within said chamber and jointly operable on said movable means, the dimensions of the aneroid and the movable means being such that the air pressure with'in the chamber exerts a force on the movable member tending to close the valve substantially equal to the force of said air acting on the aneroid in a direction to open the valve.

MILTON A. TRISLER. 

